The utility and commercial potential of quaternary ammonium compounds was recognized, for example, in U.S. Pat. No. 2,108,765 issued in 1938 to Gerhard Domagk. Subsequent research in the field further broadened the understanding, structure and utility of the antimicrobial properties of quaternary ammonium compounds in sanitizers and disinfectants for hands and surfaces. From the 1960s to the 1980s, Dow Corning Corporation, Midland, Mich., undertook the research and development of a new class of silylated quaternary ammonium compounds, which resulted in a series of U.S. patents including the following: U.S. Pat. No. 3,560,385, issued Feb. 2, 1971, discloses siliconized quaternary ammonium salts; U.S. Pat. No. 3,730,701, issued May 1, 1973, discloses the siliconized quaternary ammonium compounds as antimicrobial agents; U.S. Pat. No. 3,794,736, issued Feb. 26, 1974, and U.S. Pat. No. 3,860,709, issued Jan. 14, 1975, disclose siliconized quaternary ammonium compounds for sterilizing or disinfecting a variety of surfaces and instruments; U.S. Pat. No. 3,817,739, issued Jun. 18, 1974, discloses siliconized quaternary ammonium compounds used to inhibit algae; U.S. Pat. No. 3,865,728, issued Feb. 11, 1975, discloses siliconized quaternary ammonium compounds used to treat aquarium filters. These prior art organosilane quaternary ammonium compositions are mixtures of alkylamine starting materials, chloroalkoxysilanes, and solvents as defined by the formula:
wherein R1=hydrogen and/or C1 to C4 alkyl; R2=divalent hydrocarbon radical with C1 to C8 carbon atoms; R3=hydrogen or C1 to C4 alkyl; R4=hydrogen or C1 to C10 alkyl; R5=C8 to C22 saturated or unsaturated hydrocarbon radical and X=chloride (Cl—);C6H15ClO3Si=(3-chloropropyl)trimethoxysilane, R5—N(CH3)2=alkylamines, and CH3OH=methanol starting materials.
Prior art organosilane quaternary ammonium compounds are manufactured by reacting chloropropyltrialkoxysilanes, typically (3-chloropropyl)trimethoxysilane or (3-chloropropyl)triethoxysilane with mixtures of alkylamines, typically those that are predominantly octadecyldimethylamine, using alcoholic hydrocarbon solvents (methanol or ethanol) and various levels of heat and pressure, with or without catalysts, to enhance the speed and quality of the reaction.
Unless extensively fractionated and distilled, alkylamines are invariably mixtures of various derivatives of fatty acids (Table 2) that are converted to alkyl amines and further reacted with methyl chloride to form dimethylalkylamines; each component of which has a distinct molecular weight. Since chloropropyltrialkoxysilanes will react with each component of such amines, heretofore the commercial production of organosilane quaternary ammonium compositions actually yielded mixtures of organosilane quats. Such compositions are inherently unstable and are subject to hydrolysis, cross-linking and crystallization, with limited shelf lives.
Current commercial methodology yields organosilane quats that are only 42% or 72% active, with the balance being unreacted chloropropyltrialkoxysilanes, unreacted alkylamines and methanol. Also, these 42% or 72% active compounds are invariably flammable and/or toxic as manufactured and possibly as formulated into the ultimate end-use compositions. Their manufacturers invariably advise users that their products, even though containing 20% to 40% methanol, lack persistent storage stability and are subject to freeze/thaw degradation.
Commercially available organosilane quaternary ammonium compositions are offered by the following manufacturers, with activity levels and impurities (unreacted chloropropyltralkoxysilanes, unreacted alkylamines and solvents) as shown:
1. Dow Corning Q9-6346; Aegis AEM 5772; Piedmont Ztrex72; and Flexipel Q-1000—consisting of 72% by weight (3-trimethoxysilyl) dimethyloctadecyl ammonium chloride, 15% by weight (3-chloropropyl) trimethoxysilane, 13% by weight methyl alcohol and dimethyloctadecylamine at 1-5%.2. Dow Corning 1-6136—consisting of 42% by weight (3-trimethoxysilyl) dimethyloctadecyl ammonium chloride, 8% by weight (3-chloropropyl) trimethoxysilane and 50% by weight methanol.
All of the above compositions contain (1) methanol, a solvent that is classified as flammable under D.O.T. Label Code Flammable Liquid and transportation Packaging Group II, and which is poisonous to humans; (2) chloropropyltrimethoxysilane that is toxic to humans and animals, ignitable and requires a Flammable Liquid N.O.S. label for domestic and ocean shipping and Hazard Class 3, Packing Group III, packaging for shipment by air; and (3) alkylamines that are present in unreacted form and which themselves can have toxicological, corrosive, and storage concerns as summarized in Table 1 below:
TABLE 1PRINCIPAL HAZARDS OF METHANOL,ALKOXYSILANES AND ALKYLAMINESHazardMethanolAlkoysilanesAlkylaminesFlammableYesYesNoFlash Point54° F.52° F.>150° C.Eye IrritantYesYesYesSkin IrritantYesYesYesAvoid InhalationYesYesYesAvoid IngestionYesYesYesPoisonYesYesYesGenetically ActiveYesYesYesMarine PollutantYesYesYesReactive to AcidsNoYesYesReactive to BasesNoYesNo
Even though these organosilane quaternary ammonium compositions are generally employed in end-use formulated compositions only to the extent of 0.1 to 1.0% of the active silane quat, the presence of flammable, poisonous solvents and unreacted silanes and amines can pose hazards and undermine their shipping, storage, handling and formulation into various end-use compositions.
Methods of making organosilane quaternary ammonium compounds have been described in the patent literature, for example, in U.S. Pat. No. 3,560,385, examples 1-5 disclose the reaction of alkylamines in solvent media at elevated temperatures employing excess chloropropyltrimethoxysilane resulting in compositions equivalent to the above described commercial products with 42%-72% activity levels with unreacted starting materials and solvents. U.S. Pat. No. 3,730,701, Col. 2, lines 44-55, describes the general preparative procedure to make the C11-C22 silyl quaternary amine compounds in which a suitable solvent at ambient pressure is simply warmed with an appropriate tertiary amine and an appropriate silane. Alkylation of the tertiary amine with the alkyl halide occurs and the silyl quaternary amine compound is readily obtained. Col. 2, lines 59-68 acknowledges that the tertiary amines involved may be mixtures of long chain amines derived from natural products such as tallow, fish oils, coconut oil, etc., resulting in mixtures of silylated quaternary alkyl amines. U.S. Pat. No. 3,865,728 also discloses different amine mixtures (Col. 5, line 26 and 62) but does not specify or comment on the stoichiometry involved in the preparation of such compounds. U.S. Pat. No. 4,282,366, in Col. 3, lines 1-16, cites the Dow Corning U.S. Pat. Nos. 3,560,385 and 3,730,701 for making the silylated quaternary ammonium compounds in the conventional manner by heating the reactants at reflux temperatures in a polar solvent such as methanol, ethanol or acetone without reference to the purity or stoichiometry of the reactants. U.S. Pat. No. 4,394,378, in examples 1-2, discloses the reaction of didecylmethylamine with chloropropyltrimethoxysilane to produce organosilane quats containing unreacted silanes and solvent.
In summary, after more than 40 years, the prior art manufacturing process for making organosilane quats has remained the same. This is somewhat confirmed by the report by Donghuya University, Shanghai, Peoples Republic of China, and published in CA SELECTS, Volume 2009, Issue 23, Nov. 16, 2009. As reported, current methodology still involves the ongoing use of an excess of chloropropyltrialkoxysilanes for reaction with mixtures of alkylamines thereby resulting in organosilane quats containing unreacted starting materials and solvent. The ongoing practice of using excess starting materials (reactants) in solvents is further confirmed by a report from the College of Chemistry and Chemical Engineering, Shaanxi University of Science & Technology, Xi'an, Peoples Republic of China, and published in CA SELECTS, Volume 2010, Issue 7, Apr. 5, 2010. As reported therein, the optimal reaction for the synthesis of N, N-dimethyl-N-dodecylaminopropyltrimethoxy ammonium chloride was achieved by using the reaction medium dimethyl sulfoxide (DMSO) and a molar ratio excess of 10% of N, N-dimethyl-dodecylamine to y-chloropropyltrimethoxy silane at 120° C.
Still today, manufacturers are offering organosilane quats in concentrations of 40-72% in methanol and other solvents, which are flammable, toxic, and poisonous. Moreover, as such concentrated quats age, their viscosities, appearance, color, and compounding ability vary significantly.
The need for storage-stable, nonflammable forms of organosilane quats has been addressed most recently in U.S. Pat. No. 7,589,054, which discloses new clathrate forms of the organosilane quats which are storage-stable solids. The solid clathrates provide a new storage-stable, nonflammable, and nontoxic form of the organosilane quat. These urea-organosilane quat clathrates solve a number of problems presently confronting the use of otherwise highly-reactive quats. A clathrate form of the urea-organosilane quats overcomes the problems of lack of storage stability, handling, and shipping hazards associated with the existing 40-72% concentrations in methanol or other solvents. Nevertheless, there is still a need for new methods of making the organosilane quats so that they may be offered in a more acceptable form without the disadvantages and current problems associated with the 40-72% concentrations in methanol, as are now offered by current manufacturers.